1. The Field of the Invention
The present invention relates to a continuously variable transmission that is used to transmit torque between a power source, such as an engine or a person, and an output shaft. The speed of the output shaft varies automatically in response to the torque that is applied to an input shaft such that an infinite number of speeds between minimum and maximum are available. In particular, the present invention relates to a continuously variable transmission of a type that is suitable for use on bicycles, wherein the working diameter of the bicycle gearing mechanism is increased or decreased in response to variations in the amount of torque applied to the pedals by the rider.
2. Relevant Technology
Transmissions traditionally are used to couple a power source such as a motor to the drive train of a system or the wheels of the automobile or bicycle. Transmissions perform a gearing up or down function between the power source, such as an input shaft, and the driven member, such as an output shaft, by varying the relative rotation between the two. The relative rotation between the input shaft and the output shaft is varied through a series of ratios or gears. Previous designs of automatic transmissions have been complex arrangements that include torque converters and gears which cause the transmission to shift between a few preselected drive ratios at predetermined points. Usually, these points are clearly defined occurrences.
One application for a continuously variable transmissions has been on low horsepower devices such as bicycles, golf carts, machine tools, and wheelchairs. In general, a continuously variable transmission can be used on any machine or vehicle that is required to deliver varying torques at varying speeds. Continuously variable transmissions have also been utilized with a pulley and belt system or chain engaging surfaces that expand and contract radially.
Attempts have been repeatedly made to incorporate a continuously variable transmission on bicycles. The automatic transmission takes the place of the derailleurs. The continuously variable transmission changes the output speed ratio in accordance with the load encountered as the cyclist rides the bicycle. One problem with existing continuously variable transmissions that have been used on bicycles and include an expanding pulley or gear is that the transmission does not provide a large change in the speed ratio between the minimum value and the maximum value. In general, the existing devices that are to be used on bicycles are complex and require assembly of a large number of parts.
Some continuously variable transmissions that have been specifically designed for bicycles have utilized a gear sprocket that is configured to be able to vary its effective diameter as the chain engaging elements of the gear sprocket moves positively inward and outward. As the circumferential distance between the chain engaging elements of the gear sprocket changes, however, problems arise in keeping the chain in mesh with the elements. One attempt to address this problem has been to incorporate the use of a gear sprocket with a plurality of smaller individual sprockets mounted thereon. Each of the added sprocket wheels engage the chain. In addition, in some cases the smaller sprockets may include a one-way clutch to allow rotation of the smaller sprockets in one direction while preventing rotation in the driving direction. Other designs utilize only one sprocket wheel along with a chain tensioning idle gear. One way of eliminating the need for an idle gear is to incorporate two continuously variable transmissions. One continuously variable transmission is located at the driving source, which on a bicycle is the pedal crank, and the other at the driven member or the rear wheel. This, however, requires a complete modification of the pedal crank assembly as well as modifying the rear wheel of assembly. In fact, nearly all the available continuously variable transmissions require a complete modification of at least the front derailleur system and sometimes the rear derailleur system. As a result, available designs of continuously variable transmissions cannot be quickly and easily mounted on existing bicycles.
Another attempt to utilize a continuous variable transmission on a bicycle includes a spring loaded variable pitch sheave attached to the peddle sprocket. A v-belt couples the variable pitch sheave to a fixed sheave that is connected to the hub of the sprocket of the wheel by another chain. As the pedal torque increases, the v-belt tension is increased and the variable pitch sheave expands which causes the continuously variable transmission to shift automatically. The tension in the belt is maintained, in this case by the variable pitch sheave that has been mounted along side in the glide plate. This in turn changes the center-to-center distance between the variable pitch and the fixed sheave while maintaining a fixed distance between the variable pitch sheave sprocket and the pedal wheel sprocket.
The most popular gearing mechanism utilized on bicycles today includes a front and a rear derailleur system. These systems are complex and tend to require constant adjustment. The designs of the current derailleur systems are also prone to falling out of alignment and require frequent maintenance. In addition, the available designs of derailleurs can be slow to actuate. This slowness results in the rider being caught in the wrong gear. If a sudden increase in torque is applied to the pedals, at worst case the derailleur can become bound up and will not shift. At best case, the derailleur will require the rider to continue to pedal until the derailleur has the time to shift to the desired gear. Current derailleur configurations are actuated with remote step gears to give the rider multiple gears, in most cases twenty-one (21) gears, to choose from. For the novice rider or the leisure rider who wants to take an occasional leisurely ride on the bicycle, the complex system of multiple gears present too many choices and changing gears is too complex.
In addition, most of the derailleurs that are currently available are made up of many individual parts. In general, the current designs of front derailleur systems average approximately 25 to 40 pieces. As a result, current derailleur systems are expensive to manufacture and assemble. In addition, maintaining and adjusting the derailleur systems can be time consuming and expensive. As the complexity of the derailleur systems has increased, they have become unforgiving if they become even slightly out of adjustment.
Finally, there is a strong trend in the bicycle industry to reduce the weight of the bicycle as a whole and in particular of each component group. With the multitude of parts associated with existing derailleur systems, it is important to find ways to reduce the number of components and to cut the weight of the gearing mechanism itself.
It is an object of the present invention to provide a continuously variable transmission that is efficient and inexpensive to manufacture.
Another object of the present invention is to provide a continuously variable transmission that has a minimal number of parts.
Another object of the present invention to provide a simple, easy to use gear mechanism that automatically responds to various amounts of torque acting on the input shaft.
A further object of the present invention to provide a continuously variable transmission which is substantially a unitary member.
Yet another object of the present invention to provide a continuously variable transmission that can be incorporated into existing bicycles without requiring substantial modifications.
A further object of the present invention to provide a continuously variable transmission for use on a bicycle in which the working diameter of the gearing mechanism is increased or decreased in response to various amounts of torque being applied to the pedals by the rider.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, the present invention relates to a continuously variable transmission that comprises an input shaft to which torque may be applied, an adjustable gearing mechanism, and a driven element. The adjustable gearing mechanism is attached to the input shaft and is configured to continuously vary the drive ratio in response to the applied torque transmitted through the input shaft. The adjustable gearing mechanism includes a hub operatively connected to said input shaft, resilient arms, and an engaging portion. The resilient arms are attached to the hub. In one embodiment of a gearing mechanism, the hub and the plurality of resilient arms are integrally formed so as to form a one-piece member. The resilient arms are configured to continuously adjust the outer diameter formed by the resilient arms, thereby varying the drive ratio in response to the torque transmitted through the input shaft. The engaging portion is integral with each of the resilient arms and is configured to cooperate with an endless member such as a chain. The driven element is operably connected to said gearing mechanism by the chain. The gearing mechanism comprises material selected from a group consisting of plastic, composites including graphite fibers and fiberglass, reinforced elastomers, and metals and alloys thereof. In a preferred embodiment, the gearing mechanism comprises a plastic material.
An alternate embodiment of the present invention is disclosed in which the arms are movably attached to the hub. The arms comprise material selected from a group consisting of plastic, composites including graphite fibers and fiberglass, reinforced elastomers, and metals and alloys thereof. This embodiment of a continuously variable transmission also includes springs configured to urge the arms to resist the torque acting on the gearing mechanism.